I don't think this would work. I haven't read that part of the code, but I believe you still have to slurp the entire document in memory with XMLin and process it before you start emitting SAX events using XMLout.

What could work is using a SAX parser, and setting up a SAX filter that would spur out messages before passing the data untouched to XML::Simple. Or even using a tee like XML::Filter::Tee so that both XML::Simple and a separate SAX handler receive the input. That handler can then spit out a message depending on where it is in the parsing.

OTOH playing with signals to send an "everything is OK" message every x second might be quite simpler ;--)